Because enzymes can catalyze chemical transformations so effectively, there is increasing emphasis on the use of enzyme reactions in commercial processes. The relatively high cost of enzymes demands their reuse. Typically, if the reaction is performed under homgeneous conditions recovery of enzyme is difficult and expensive, which effectively precludes homogeneous enzymatic catalysis. The solution to this problem is to insolubilize enzyme under conditions where a substantial portion of the enzymatic activity exhibited in solution remains under heterogenous reaction conditions.
One particular solution to the aforementioned problem is the construction of immobilized enzyme systems. An immobilized enzyme system consists of a support matrix to which there is bound an enzyme. A support matrix is a structure characterized as having good physical integrity and favorable properties toward liquid flow under conditions experienced in fixed bed reactors, and further characterized by having the ability to bind or immobilize enzymes with minimum perturbation of enzymatic action. By an immobilized enzyme system is meant the structure which results from immobilization of an enzyme on a support matrix.
The binding or immobilization of enzymes to a support matrix is represented by the extremes of physical and chemical binding forces. It is to be recognized that in most cases enzyme immobilization arises from a combination of such binding forces, although often one such force predominates, with the nature of enzyme immobilization generally being determined by the nature of the support matrix. As an example, when the support matrix is a resin, such as one of the phenol-formaldehyde type, binding is predominantly through physical forces. A similar result is obtained when the support matrix is of an ion exchange type. Where the support matrix is comprised of refractory inorganic material, such as inorganic oxides, glass, and ceramics, bearing or impregnated with organic material, for example, polyamines, either bearing pendant functional groups themselves or cross-linked with a bifunctional reagent which provides pendant functional groups, enzyme immobilization arises mainly by chemical reaction of a site on the enzyne with the pendant functional group so as to form a covalent bond. In such an instance binding is, at least predominantly, by chemical means.
The support matrix of U.S. Pat. No. 4,141,857, which enjoys wide commercial utility, is an inorganic porous support impregnated with a polyamine cross-linked with an excess of a bifunctional reagent so as to afford pendant functional groups. In such a support matrix the amino groups are in the backbone of the polyamine, that is, where polymeric amines are used the amino groups are part of the polymer chain.
In contrast, the patentees of U.S. Pat. Nos. 4,193,910, 4,206,259, 4,218,363, and 4,250,080 describe a support matrix where the amino groups of the polyamine are pendant to a polyethylene polymer backbone which is completely nonpolar and highly hydrophobic.
In some applications it is desirable to have a support matrix where the amino groups are pendant to a polymer backbone which is hydrophilic, but which otherwise retains the features and advantages of the previously described support matrices. The support matrix of this invention provides the attributes of a polar, hydrophilic polymer bearing pendant amino groups, which is a combination unknown in the prior art.
The invention described herein relates to support matrices, and immobilized enzyme system therefrom, comprising an inorganic porous support impregnated with a polymer having a hydrophilic backbone and bearing pendant polyamines which are cross-linked with dialdehydes, and whose amino groups bear pendant aldehyde groups. One advantage of the instant invention arises because the polar and hydrophilic polymer presents a different, generally more natural environment to a subsequently bound enzyme than is the case where the polymer is nonpolar and hydrophobic. Another advantage of the invention described accrues from the pendancy of the polyamines which themselves bear pendant aldehyde groups ultimately engaged in covalent bonding to enzymes, resulting in the enzyme being further away from the surface of the support matrix than is the case in prior art materials and thereby presenting an environment more closely analogous to that of soluble enzymes than was previously possible.